1. Field of the Invention
The present invention relates to a direct-fuel-injection-type spark-ignition internal combustion engine.
2. Description of the Related Art
There has heretofore been known stratified charge combustion produced by directly injecting fuel into a cylinder to form a mixture that can be favorably ignited (combustible mixture) only in the vicinity of a spark plug, at the ignition timing, to burn a lean mixture in the cylinder as a whole. To carry out the stratified charge combustion, in general, fuel is injected in the latter half of the compression stroke. It is intended that the thus injected fuel proceeds into a concave combustion chamber, is vaporized by robbing heat from the wall surfaces of the combustion chamber, is deflected by the shape of the combustion chamber toward the spark plug, and forms a combustible mixture near the spark plug.
In general, the fuel injection valve injects fuel in a shape that is conically concentrated. Therefore, a relatively long period is required while the fuel injected in the last stage of fuel injection becomes a combustible mixture utilizing the heat from the wall surfaces of the combustion chamber. To ensure this period, therefore, the fuel injection end timing must be advanced. An amount of fuel which can be injected in the latter half of the compression stroke, therefore, inevitably decreases, and stratified charge combustion must be abandoned in high engine load operations in which a relatively large amount of fuel is required. It has therefore been desired to carry out stratified charge combustion, which is effective in decreasing the consumption of fuel, over a wider range of engine operations.
Japanese Unexamined Patent Publication (Kokai) No. 9-158736 proposes injecting the fuel in the shape of a flat fan having a relatively small thickness by using a fuel injection valve having an injection hole in the shape of a slit. The thus injected fuel can rob heat from a wide area of the wall surfaces of the combustion chamber, making it possible to form a combustible mixture within a short period and to retard the timing for ending the injection of fuel. Thus, it is expected to increase an amount of injected fuel in the latter half of the compression stroke and to expand the region of stratified charge combustion toward the high engine load side.
In the above-mentioned related art, the fuel injected in a flat fan shape spreads in the width direction while progressing along the bottom wall of the combustion chamber. The side wall of the combustion chamber has a circular arc shape, in plan view, so that when the spreaded fuel moves up along the side wall of the combustion chamber, each part of fuel is converged toward the center of the side wall. Thus, a mass of combustible mixture is expected to be formed in the vicinity of the spark plug. Undoubtedly, if the side wall of the combustion chamber has a circular arc shape, each part of the spreaded fuel in the width direction is given a speed component toward the center of the side wall. However, all parts of the fuel do not necessarily move to the same position and thus a mass of combustible mixture may not be formed in the vicinity of the spark plug. Therefore, misfiring can occur.
Accordingly, an object of the present invention is to provide a direct-fuel-injection-type spark-ignition internal combustion engine in which fuel is injected in a flat fan shape having a relatively small thickness, and which can prevent misfiring in stratified charge combustion.
According to the present invention, there is provided a first direct-fuel-injection-type spark ignition internal combustion engine comprising: a spark plug, a cavity formed on the top surface of the piston, and a fuel injection valve for injecting fuel into the cavity in nearly the shape of a fan having a relatively small thickness, wherein the side wall of the cavity facing to the fuel injection valve, for leading the fuel to the vicinity of the spark plug, has a horizontal sectional shape consisting of a part of an ellipse shape of which two foci are at a position of the injection hole of the fuel injection valve and a position near to the spark plug in plan view, and the side wall has a deflecting portion to deflect said fuel toward the inside of the cavity.
According to the present invention, there is provided a second direct-fuel-injection-type spark-ignition internal combustion engine comprising: a spark plug, a cavity formed on the top surface of the piston, and a fuel injection valve for injecting fuel into the cavity in nearly the shape of a fan having a relatively small thickness, wherein the side wall of the cavity facing to the fuel injection valve, for leading the fuel to the vicinity of the spark plug, has a horizontal sectional shape consisting of a part of a parabola shape of which the focus is at a position near to the spark plug in plan view, and the side wall has a deflecting portion to deflect the fuel toward the inside of said cavity.
According to the present invention, there is provided a third direct-fuel-injection-type spark-ignition internal combustion engine comprising: a spark plug, a cavity formed on the top surface of the piston, and a fuel injection valve for injecting fuel into the cavity in nearly the shape of a fan having a relatively small thickness, wherein in the side wall of the cavity facing to the fuel injection valve, for leading the fuel to the vicinity of the spark plug, both end portions thereof have a horizontal sectional shape consisting of a part of an ellipse shape of which two foci are at a position of the injection hole of the fuel injection valve and a position near to the spark plug in plan view, a center portion thereof has a horizontal sectional shape consisting of a part of a parabola shape of which the focus is at a position near to the spark plug in plan view, and the side wall has a deflecting portion to deflect the fuel toward the inside of the cavity.
The present invention will be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings.